Battery units including rechargeable batteries as previously constructed usually were self-contained units to which a transfer switch was electrically connected by wires and remotely located. Usually, the battery was held in a long tube, clipped to a frame portion of the bicycle, for example beneath the horizontal frame bar or alongside the saddle support post. The operator of the bicycle had no opportunity to monitor the charge state of the battery or the function of the lights energized thereby, and particularly to be assured that the tail light is operative.